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Old 07-08-2008, 08:37 PM   #1
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So much potential....

Hi everybody. I think this site is just what I've been looking for. I've spent a lifetime modifying nearly every car that I've owned to get more power, and now I've decided to tackle a fuel sipping gas miser. Kind of a change of direction for me, but it should be a fun endeavor.

Anyway, I just picked up an '88 Honda CRX DX (automatic) to use as rolling stock. This is pretty much the lowest FE version of the CRX family, but I still managed to get 46 mpg highway on a recent road trip from Albuquerque to Flagstaff (that's 325 miles, gaining 2000 ft altitude and ending up at 7000 ft asl), so I figure I've got a chance of doing some good things with the car.

For starters the auto trans has got to go. I've got my eye open for either a standard DX or an HF trans to go into it. But I'm open to suggestions on what else to do. Any suggestions and hints will help.... especially if they're vehicle specific.

By the way, the car has about 180K on it right now and it still runs like a top. I'm not planning on replacing the engine unless I find a deal on an engine/trans combo. But changes in the efi, either to another stock system or maybe even a standalone (I've got an MS system sitting on the shelf) system isn't out of the question. A cheap low boost turbo system may be in the cards as well. I think I have the disclipline to keep my foot out of it if I go that route.....

Anywho, thanks in advance for all the good advice I'm sure you're all about to bestow on me
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Old 07-09-2008, 04:35 AM   #2
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another cool toy is the scangauge which will tell you your MPG in realtime. you can't use it because it only works for '96 and newer cars with the OBDII port but there are other options out there. I don't know what they are because all my vehicles are 96 or newer.

just figured I'd put that bug in your ear about it. you could read up on it. I have a truck that will do a 14.5sec qtr (not bad for a truck) so I know what you mean about keeping your foot out of it. the scangauge helped me a lot because I could see what affect my driving had on the MPG.

I have also heard of people swapping in the VX motors into the CRXs to get lean burn. other models have lean burn as well. good luck to you and the manual tranny is a good idea too. I am stuck with an auto and don't want to put the time or effort into changing. sometimes it costs to be a lazy man.

OH and welcome to the site
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Old 07-09-2008, 06:44 AM   #3
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Hi!

I'm not totally convinced that a manual tranny is always best, particularly if you end up with with the same or lower final drive with a manual. In city driving, practically any standard will save a bunch, but if it stretches it's legs on the highway much, I'd look carefully at the options for the final drives. Modifying automatics with severe duty shift kits appears to me to take quite a chunk of inefficiency out of them, for instance with the shift kit mods on my auto, from 0-60 times vs stock I appear to have gained 10HP at the wheels, this would be about 7% of the power output, so drivetrain loss now has to be in the range for a manual.

Of course the manual allows some highly efficient techniques that the auto doesn't, but if you've got a pure highway pound with heavy traffic, that sort of thing is gonna be difficult to do.

I was rather shocked when I found that a number of 5 speeds are needing over 3000RPM to cruise at 60, my 3 speed auto with the TC locked up takes just ~2600.
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Old 07-09-2008, 07:04 AM   #4
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Quote:
Originally Posted by Hal9000 View Post
changes in the efi, either to another stock system or maybe even a standalone (I've got an MS system sitting on the shelf) system isn't out of the question.
MegaSquirt, you say? Cool.

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Originally Posted by BEEF View Post
another cool toy is the scangauge which will tell you your MPG in realtime. you can't use it because it only works for '96 and newer cars with the OBDII port
Hmm...does MegaSquirt do OBDII?
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Old 07-09-2008, 07:11 AM   #5
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Quote:
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I was rather shocked when I found that a number of 5 speeds are needing over 3000RPM to cruise at 60, my 3 speed auto with the TC locked up takes just ~2600.
What? My minivan (Hyundai Entourage) is barely scraping 2000 RPM at 60MPH. I can run in 5th gear at 45MPH @ 1100RPM. It has a 5 speed auto "with manual-shift gate". I don't generally use the manual feature.
(I don't put the Hyundai in the garage w/gaslog because lots of other people drive it, and it tends to get 14-15MPG because they can't keep their foot off the d$%m pedal).

My previous ride (a VW Jetta Wagon TDI) would be around 2200RPM at 60MPH, IIRC. I know it was well over 3000 @ 80MPH and pushing 4k @ 110MPH. Redline was low, around 4500-5000. No, I don't drive that fast anymore.

Man, I miss that car, but I don't miss replacing the starter every 9 months, and other electrical parts around every 10000 miles.
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Old 07-09-2008, 07:15 AM   #6
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My VW is 3000rpm at 70mph, and in a similar discussion on another forum folks are reporting 4000rpm at 70mph for Hondas.
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Old 07-09-2008, 07:27 AM   #7
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Well obviously there are 5 speeds with decent ratios, I was just saying to research them, rather than blindly rushing into a "5 speed is always better" trap.
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Old 07-09-2008, 07:28 AM   #8
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If you're modifying a CRX, a question & a few suggestions.

1) Does it have door-mounted seatbelts? If not, you've got the early 88 version and it's lighter, a plus. If not, oh well.

2) Put in a VX engine and start with an HF transmission.
3) Once that's done, modify a Honda Civic Wagovan transmission for even better results. Wagovan is a 5-speed plus granny gear. Can be modified to turn into a 6-speed. Start with the 1st gear from an Si and end up with a .55 "6th" gear, HF final drive. Will give you most power with the VX engine D15Z1 and the Wagovan modified transmission. You should be able to turn out MPG over 80 with this setup.
4) Lighten the vehicle as much as you can - carbon fiber or aluminum hood, doors, etc., but make sure safety is not compromised. Use a donut spare in the trunk, etc.

Good luck!
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Old 07-09-2008, 08:04 AM   #9
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Welcome to the club of former Honda power modders now turned FE modders!

101mpg: Hm, my 90 Si had door mounted seatbelts. Wasn't a CRX though.

Most Hondas (except the VX) run about 3000 RPM @ 70 mph, 3500 @ 75, and 3800 @ 80mph. That has been my experience with 4 and 5 speeds, manual and automatics. RPMs are not always bad for FE. Sure, if that were a Mustang, those would be ridiculously high RPM and you'd be wasting gas. But on a Honda with a 7000 redline, airflow through the engine at 3000 RPM has been tuned for efficiency (but not volumetric efficiency). If you were to modify the final drive to the point that you were cruising at 2000 RPM I guarantee you would lose FE (mainly because it would require more throttle to keep the car at speed). Again, the VX is an exception.
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Old 07-09-2008, 08:34 AM   #10
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you would lose FE (mainly because it would require more throttle to keep the car at speed).
More throttle would merely reduce pumping losses and shouldn't reduce FE.
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